With the progress of grouping technology, a conventional circuit-switched telecommunication network is developing towards a packet-switched broadband telecommunication network, and a Session Initiation Protocol (SIP) serving as call control signaling of a packet telecommunication core network is among current developing trends of the technology. For example, in the research of a Next Generation Network (NGN), standard organizations, for example, the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) and the European Telecommunications Standards Institute (ETSI), all adopt an IP multimedia subsystem (IMS) network architecture defined by the Third Generation Partnership Project (3GPP) as a core network of the NGN.
The IMS defined by the 3GPP is a target network in the Third Generation (3G) mobile communication network for implementing packet voice and packet data and providing unified multimedia services and applications. The IMS adopts an IP packet domain as a bearer channel for signaling control and media transmission, and adopts the SIP as call control signaling to realize the separation of service management, session control, and bearer accessing. The SIP with its core component defined by the Internet Engineering Task Force (IETF) is an application-layer control protocol for establishing, modifying, and terminating a multimedia session or call. The multimedia session includes a multimedia conference, tele-education, an IP phone call, and the like.
With the increasing progress and commercial applications of the IMS technology, operators have considered the evolution of a conventional public switched telephone network (PSTN) to an IMS network, and a conventional plain old telephone service (POTS) end user is enabled to get access to the IMS network.
However, the POTS terminal adopts a dialing mode of overlap sending, that is, once a user dials digits, the POTS terminal transfers the digits to the network. While the SIP over the IMS network supports enblock sending, that is, after the user dials all the digits, the SIP transfers the called digits to the network at a time. Therefore, when the POTS terminal accesses the IMS network, the IMS network needs to support the overlap sending.
Currently, no appropriate technical solution is provided in the prior art to enable the IMS network to support the overlap sending. Further, in the IMS network in the prior art, when a call connection fails due to an incomplete address of called user identification (ID) information resulting from the overlap sending, the calling network may not be informed about the reason of the call connection failure, thus leading to the call connection failure.